In human anatomy, the vertebral column (i.e., backbone or spine) is a column typically consisting of bones and tissue, including 33 vertebrae, situated in the dorsal area of the torso. The vertebral column serves to house and protect the spinal cord in a spinal canal.
Occasionally, abnormalities, disease, trauma, and so forth can cause a spinal column disorder. One type of spinal disorder includes spinal deformity. Deformities include spondylolilsthesis, retrolisthesis, kyphosis, and scoliosis. Spondylolisthesis is an anterior or forward slip of one vertebra on another. In contrast, retrolisthesis is a posterior displacement of one vertebral body with respect to the adjacent vertebral segment. Kyphosis is an exaggerated kyphotic (posterior) curvature in the thoracic region that produces a “hump back”, a condition commonly observed in osteoporosis. Scoliosis is a rotational deformity of the spine, and in adults, may include a lateral displacement as well known as lateral olisthesis. Scoliosis the most common abnormal curvature, occurring in 0.5% of the population. It is subdivided into degenerative scoliosis, which affects adults, and various forms of pediatric scoliosis, the most common of which is adolescent idiopathic scoliosis.
Spinal column disorders can result in significant pain as well as diminished nerve function. Some spinal column disorders are addressed using a spinal fixation technique. In spinal fixation, implants are used for fusing or immobilizing adjacent vertebrae. Spinal fixation can improve the position of the adjacent vertebrae relative to one another and can alter the overall alignment and/or curvature of the spine. Spinal fixation or instrumentation can immobilize the spine internally in order to promote fusion between vertebrae. Fusion is a process which can take up to several months or a year.
One spinal fixation technique includes using orthopedic contouring rods which run generally parallel to the spine. This technique often involves an invasive surgical procedure to expose the spine and attach pedicle screws to the pedicles of the appropriate vertebrae. The pedicle screws are configured to receive the orthopedic contouring rod which can be bent to achieve the desired curvature of the spinal column.
Traditionally, pedicle screws have been inserted through one major central incision, where muscles and other tissues are dissected off of the spine and retracted to the side to facilitate visualization of the deep spinal bones. Under direct visualization, with or without radiological imaging, pedicle screws are placed into the pedicles of the vertebral bodies, and then rods are typically placed to connect pedicle screws from one bone to those of other bones through the tulip. Since there are two pedicles for each vertebral body, one on the right and one on the left, a construct will most typically have two rods, one which connects pedicle screws on the right side, and another that connects pedicle screws on the left side. When the screws and rods are placed through this central incision, surgeons visualize the anatomy well, but at the cost of significant stripping of the muscle tissue which then is scarred, often devascularized, and potentially a source of pain in the future for the patients. Hence, the large, open exposure causes some disability or harm to the patient.
In contrast, if pedicle screws are placed through tiny incisions with reliance on radiographic visualization, not direct visualization, surgeons can instrument the spine with minimal muscle and tissue destruction. In other words, percutaneously placed pedicle screws can potentially save the patient the significant trauma caused by the traditional open exposure of the spine through the central incision. Unfortunately, in long constructs where several pedicle screws are inserted through percutaneous techniques, contouring a rod that will fit into the patient's anatomy can be difficult since a trial malleable rod cannot be trialed into the tulips under direct visualization. Typically with long constructs done percutaneously, contouring the rod can take significant amounts of time, as the rod often is passed through a small incision a the top of the construct, removed, contoured differently, passed again, and recontoured until the rod is fully contoured. The process of contouring the rod takes significant amount of time that, if diminished, could lead to shorter patient operative time, less anesthesia, less blood loss, less risk for complications, and better patient outcomes.
Improper alignment and inaccurate bending of the contouring rod decreases the effectiveness of the spinal fixation and can increase surgical difficulty and time expenditure. In combination with the incisions involved in for the installation of the contouring rod, extended surgical procedures and related difficulties or complications are generally recognized as major contributing influences for extended patient recovery and sub-optimal spinal fixation results.